Preparation Of T-Nb₂O₅ And Its Application In Potassium Ion Batteries

The scarcity of lithium resources,uneven distribution and increasing lithium consumption year by year result in the high price of lithium ion battery?LIBs?,which limits the application of LIBs in smart grid and other large-scale energy storage systems.Among alkali metals,K is abundant,widely distributed and cheap in the earth's crust,and its physicochemical properties are similar to Li,and the standard electrode potential of K⁺/K is similar to Li⁺/Li.These advantages make it possible for potassium ion batteries?KIBs?to be applied in the field of large-scale energy storage.However,due to the large potassium ion radius and slow diffusion kinetics,the efficiency and stability of potassium ion batteries are poor.At present,the research on the anode and cathode materials of potassium ion batteries with rapid reversible reactions is a hot topic among researchers.Orthogonal niobium pentoxide?T-Nb₂O₅?,with its unique properties of layered structure,open framework and good chemical stability,has attracted wide attention as an electrode material for lithium batteries and supercapacitors.The?001?crystal surface of T-Nb₂O₅ has a large lattice spacing?0.39nm?,which can accommodate large radius cations such as Na⁺and K⁺,which is conducive to rapid diffusion.However,the study of T-Nb₂O₅ as a negative electrode of potassium ion battery and its working mechanism have not been reported.In this thesis,T-Nb₂O₅ with micro-nano hierarchical structure was prepared by hydrothermal synthesis method,and feasibility as the anode material for KIB and potassium-based dual ion battery was further studid.Therefore,insufficient dynamics of intercalation-type anode and the problem of electrode pulverization caused by volume expansion of alloy-type anode for dual ion battery have been solved,and the cycle and rate performance of dual ion battery have been enhanced.The research content of this paper is mainly divided into the following two parts:?1?T-Nb₂O₅ with micro-nano graded structure was synthesized by hydrothermal method and used as anode material for KIB,and the mixed potassium storage mechanism of T-Nb₂O₅ material containing intercalation and pseudocapacitance behavior was discussed in detail.Due to the rapid diffusion behavior and the synergistic effect of layered nanostructures,T-Nb₂O₅ shows excellent potassium storage performance with specific capacity of 104 mAh g^-11 at the current density of0.4 A g^-1,and a capacity loss of 0.068%at each cycle of 400 cycles.?2?Furthermore,utilizing the T-Nb₂O₅ nanowires as the anode,a novel potassium dual-ion battery?KDIB?was fabricated,which exhibited high rate performance with81 mA h g^-11 even at 30C?91%capacity retention?,and also achieved excellent cycling stability with a capacity retention of 86.2%after 1000 cycles at 20C,which is the best result for KDIBs reported so far.In addition,by characterizing the electrodes before and after cycle,we explored the reaction mechanism of the dual ion battery and the insertion/release behavior of K⁺and anions in the anode and cathode respectively,and further explained the reason for excellent electrochemical performance of the dual ion battery.